Power modules on space system have long been used to charge onboard batteries and provide power to system loads. Referring to FIG. 2, the power transfer from an array of solar cells to a battery is a function of temperature and sunlight illumination. The temperature is shown to have a range between 95° C. degrees to 15° C. degrees, having a nominal temperature of 55° C. degrees. A battery can be charged in three power modes including direct energy transfer (DET), boost peak power tracking (PPT), and buck PPT. During the DET mode, the power module connects source array to the battery and load for high efficiency. Peak power tracking (PPT) mode is used during high and low array voltages in response to varying temperature and illumination conditions for maximum source power but power efficiency transfer is lower due to switching and controller losses.
The PPT has two operating conditions, boost PPT and buck PPT. Power module utilization of DET, buck PPT, and boost PPT modes as a function of array temperature is well known. DET is effective at nominal temperatures when the maximum power voltage of the array is near the battery charge voltage. Buck PPT is implemented when the array is cold and the maximum power voltage is significantly higher than the battery charge voltage. Buck PPT decreases the voltage from the array to the battery. Boost PPT is used at high temperatures when the maximum power voltage of the array is significantly lower than the battery charge voltage. Boost PPT increases the voltage from the array to the battery.
Power modules have been used on miniature satellites but suffer from power losses associated with PPT switching. Switching power losses are disadvantageously significant relative to overall power. The DET is more advantageous much of the time but not under all conditions.
U.S. Pat. No. 6,713,989 teaches a solar switch, by Reynolds, and discloses an electronic switch that maintains full conduction between solar array and battery during charging. Efficiency is high in this simple technique because losses associated with power switching and complex controls are eliminated. However, maximum source power is not continuously extracted by this DET method because array voltage is equal to varying battery voltage. The influence of array temperature and degradation to power generation is neglected.
U.S. Pat. No. 4,794,272 teaches a power regulator utilizing only battery current monitoring, by Bavaro, and discloses a PPT method to extract maximum array power. However, power dissipation is significant because the switching converter and control circuit are continuously active. Therefore, less power may be delivered to the load or battery than the DET mode despite maximum power being extracted from the solar array.
U.S. Pat. No. 6,469,476 teaches a multimode converter for a motor vehicle electrical system, by Barrett, and discloses a power system with multiple operating modes. However, the system is designed specifically for motors and is not directly applicable to other systems such as solar power. The converter disadvantageously has an excessive component count. A control unit of the converter is not described as including a low power standby mode for power conservation.
Converters have long been used in regulated power supplies. Converters are supplied in compact packages but are unsuitable of DET. Existing power modules disadvantageously suffer from PPT switching losses, excessive component count, exclusive continuous high power operation without entering standby modes, and stand alone connections between a power source and loads. These and other disadvantages are solved or reduced using the invention.